JPH01259118A - Rough material for press forming - Google Patents

Abstract

PURPOSE:To obtain the rough material for press forming which is locally reinforced without impairing the formability by impressing high-density energy to the required section on the rear surface of a plate material and subjecting this section to a rapid remelting-rapid resolidifying treatment, thereby locally forming a finer-grained crystal layer. CONSTITUTION:The plate material 3 to be made into the rough material for press forming is placed on a base plate 1 in which cooling water 2 is previously passed. The required section of the surface which is to be used as the rear surface of the product after the press forming of the plate material 3 is irradiated by a laser beam 6 while a laser torch 4 is properly moved in an arrow direction and a shielding gas 8 is injected. The finer-grained crystal layer 7 consisting of the rapidly remelted-rapidly resolidified beads in thus formed in the above-mentioned section. The rough material for press forming reformed only in the part for which strength, etc., are required is thereby obtd. without impairing the formability and increasing the weight.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This optical fiber is related to plate-shaped rough materials used by press forming, such as automobile body outer panels.

Conventional technology In general, the outer skin of an automobile is required to have high tensile rigidity and to have excellent tent resistance, that is, to minimize dents that would remain as permanent deformation when pressed with fingers, etc. It is required to have the property that it will not occur. In addition, since the body outer panels of automobiles are used after being press-formed, they have good press-formability.
It is also required that no wrinkles or cracks occur during press molding.

By the way, as a conventional car body outer panel, 5CP28
Mild cold-rolled steel sheets such as 5CP28 materials have been used in many cases, but cold-rolled mild steel sheets such as 5CP28 materials have good press formability, but the yield point of the material is low, so the tensile rigidity and In order to improve the tent's resistance, it is necessary to use a thicker plate or to put an inner layer (reinforcing material) on the inside. On the other hand, in order to improve tensile rigidity and tent resistance, high tensile strength steel plates having particularly high strength among cold-rolled steel plates are increasingly being used.

Problems to be Solved by the Invention When a cold-rolled mild steel sheet such as 5CP28 as described above is used and its wall thickness is increased, the weight increases, which is a problem that goes against the goal of reducing the weight of automobiles. Furthermore, when an inner layer is used, there is a problem in that the weight increases as well.

On the other hand, when high-strength steel plates are used, not only does the material cost increase, but their low elongation makes them prone to cracking during press forming, making deep drawing difficult and shortening the lifespan of the cutting blades. In addition, when using high-strength steel plate scrap material as return material, Mn
, P@ is high in content, so there is a problem that castability is adversely affected.

This optical fiber was created against the background of the above-mentioned circumstances, and has been developed for areas that require tensile rigidity and tent resistance, as well as areas that require strength in press molding, without impairing moldability or increasing weight. The object of the present invention is to provide a press-forming material that solves the above-mentioned problems at the same time by locally strengthening the material.

Means to Solve the Problem In this Hikari press-molding material, rapid remelting and rapid resolidification are applied to the necessary parts of the surface that will be the back side of the product after press molding, that is, the parts that need to be strengthened. It is characterized in that a crystal refinement layer is locally formed.

Action Rapid remelting - Rapid resolidification treatment applies high-density energy such as laser, TIG arc, plasma arc, or electron beam to the surface of a metal material to rapidly remelt the surface layer.
Subsequently, the application of high-density energy is stopped or the position of the mark is moved to cause rapid re-solidification,
Since the resolidification in this process is achieved by rapid heat transfer to the base metal (unmelted portion), the solidification rate is extremely high.

Therefore, the portion subjected to this treatment becomes a crystal-refined layer in which the crystal grains are significantly finer than before the treatment. The structure in which the crystal grains are refined in this manner has higher hardness than the base material structure, and its strength also increases.

This Hikari press molding material is rapidly remelted.
A crystalline fine layer is formed locally due to the rapid resolidification process, and the area near where the crystalline fine layer is formed is strengthened as described above, improving tensile rigidity and Punt resistance. There is. On the other hand, since the crystalline refinement layer is formed locally only in the necessary parts of the rough material for press forming, by using a soft steel material such as 5CP28 with elongation as the material for the rough material, it is possible to As a whole, the moldability necessary for press molding such as elongation can be sufficiently ensured.

In other words, by using a material with good formability to ensure press formability, and preventing cracking during press forming, by forming a locally refined crystal layer in the necessary areas. This makes it possible to improve the tensile rigidity and tent resistance of that area.

On the other hand, in the case of raw material with a low yield point such as mild steel materials, the amount of raw material flowing in during press forming may be excessive and wrinkles may appear, but only in areas where there is a lot of tension, as mentioned above. By forming a crystal-refined layer through rapid remelting and rapid resolidification treatment to improve the yield point of that region, wrinkles can be prevented.

EXAMPLE FIG. 1 shows an example of a situation in which the rapid remelting-rapid resolidification process applied in the production of the press-molding rough material of the present invention is carried out.

In FIG. 1, cooling water 2 is circulated inside a base 1 in advance, a plate material 3 to be used as a press-molding material is placed on the base 1, and a laser beam 6 is applied to the plate material 3 by a laser torch 4. The laser beam irradiation position is continuously moved by moving the laser torch 4 or the base 1 in the direction of the arrow 5 while irradiating the surface of the laser beam. The surface layer of the plate material 3 is rapidly melted by laser beam irradiation, and the melted layer is rapidly resolidified by moving the laser beam irradiation position, thereby forming a remelting-resolidifying bead 7. This remelting--resolidifying bead 7 portion--corresponds to crystal refinement in the present invention. Note that in FIG. 1, 8 represents a shielding gas.

In the press-molding material of the present invention, the region where the remelting-resolidifying bead 7, that is, the crystal refining layer 7 formed by the rapid remelting-rapid resolidifying process, is formed in a localized area selected as necessary. Any part may be used, and the planar shape of the crystal-refined layer 7 may be determined as necessary.
Usually, it is sufficient to form a crystalline fine layer in the form of a straight bead as shown in FIG. 2, or to form a fine crystalline layer in the form of a spot bead as shown in FIG. In Figs. 2 and 3, the reference numeral 10 indicates a blank material for press molding.

Regarding the cold rolled steel plate with a thickness of 0.8 mm made of 5CP35,
FIG. 4 shows a cross section of the rough material in the vicinity of the bead formation area when a linear bead (crystalline fine layer) is formed by the rapid remelting-rapid resolidification process using a laser beam as described above. A photograph of the cross-sectional structure of the crystal-refined layer is shown in Figure 5.
A photograph of the cross-sectional structure of the untreated base metal portion is shown in FIG. In this process, the laser output was set to 1.5 rhymes, and the torch feed speed was set to 800 mtnl.

As is clear from the comparison between Figures 5 and 6, the crystal refinement layer (Figure 5) produced by the rapid remelting-rapid resolidification treatment is significantly different from the untreated base metal portion (Figure 6). Crystal grain size is 1/4 ~
The micro-Vickers hardness (mHv) of the micro-Vickers hardness (mHv) of the micro-Vickers hardness (mHv) was found to be approximately mHvllo for the base material shown in Figure 6, while the crystal fine layer shown in Figure 5 It was found that mHv was about 150 and FHV was improved by about 40. This increase in hardness is due to
As is clear from the microstructure photograph in FIG. 5, this is not caused by precipitation of carbides or martensitic transformation, but is caused by refinement of crystal grains.

Furthermore, a cold-rolled steel sheet made of 5CP2SDY material with a thickness of 0.8 Ayu was subjected to rapid remelting and rapid resolidification treatment using a laser beam in the same manner as described above to form a crystal fine layer. The results of the test are shown in Table 1. For comparison, tensile tests were also conducted on untreated 5CP2aDY material and higher strength 5CP358H material (untreated), and the results are also shown in Table 1.

The processing conditions were laser output i, skw, and torch feed rate 6001N#I/mi, and the shape of the test piece was as shown in FIG. 7, the width of the parallel part w1 = 2541. Length of parallel part f+=150 mm, width of bead (crystalline refinement layer) 7 due to rapid remelting-rapid resolidification treatment w2 = 2.5 mm, length of bead 7! ! 2 = 1701 m, and two straight beads 7 are formed in parallel.

Table 1 As is clear from Table 1, Honko Meigetsu (Honko Meigetsu) in which a crystal refinement layer was formed by locally applying rapid remelting and rapid resolidification treatment.
The base material (5CP2aDY material) has improved tensile strength by about 10%, yield point by about 30%, and elongation by about 15% compared to the pretreated base material. This strength is 1
It is comparable to 5CP35 or 5CP35BH materials in its class, and has a higher elongation value than the 5CP35 class.

Please note that the absolute values of this Komyo material shown in Table 1 are just examples, and may vary depending on the type of base material, rapid remelting/rapid resolidification treatment conditions, and even the base material. ! The material properties differ depending on the volume of the crest, etc. In other words, material properties can be selected to some extent by combining base materials and processing conditions.

Figure 8 (A) shows an example of a press molding material to which this light gap is applied to improve press formability, especially to prevent wrinkles and distortions from forming during press molding, and Figure 8 (B) )
Figure 2 shows the conditions during press forming of the raw material.

The press forming material 10 shown in FIG.
As shown in Figure (B), the area 11 where wrinkles should be suppressed during press molding and the area 12 where the tensile stress during press molding is large and noticeable are preliminarily treated by rapid remelting and rapid resolidification treatment. A crystalline fine layer 7 in the shape of a straight bead is formed so as to extend in the flow direction (pulling direction) of the material during press molding. In such a press-forming material, the tension of the material in the direction of the arrow 131,000 created during press-forming is restrained by the high-strength crystal-refined layer 7, and the tension of the product 15 after press-forming is improved. Photogenic wrinkles and distortions are prevented. In addition, 6 and 16 in FIG. 8(B) indicate a press lower die.

Figure 9 (A) shows an example of a blank material for press forming to which the present invention is applied to improve the tension rigidity and tent resistance of pressed products, and Figure 9 (B) shows the blank material. This shows the situation after press forming.

In the pressed product 15 shown in FIG. 9(B), for example, improvement in tensile rigidity or tent resistance is required at the portion 17, so the press-forming material shown in FIG. 9(A) is also required. A plurality of linear bead-shaped crystal finer layers 7 are formed at locations corresponding to the portions 17 by rapid remelting and rapid resolidification processing.

FIG. 10 shows the external shape of an automobile, and the parts 21A to 27 that require tent resistance and tension rigidity are formed in the body outer panel parts (press molded parts) 21 to 27.
A is shown with cross hatching. Here 21
represents the hood, 22 represents the two parts, 11 = entrance, 23 represents the roof, 24 represents the front door, 25 represents the rear door, 26 represents the luggage, and 27 represents the quarters. In addition, by forming a linear or dot-like crystal refinement layer by rapid remelting and rapid resolidification treatment on the back side of the portion corresponding to each portion 21A to 27A in l15, each portion 21A to 27A is It is possible to significantly improve the tensile strength and punt resistance.

In the above-mentioned example, a cold-rolled steel plate was used as the base material for press forming, but it goes without saying that the present invention can be applied not only to steel plates but also to cases where aluminum alloy plates or the like are used as the base material. Further, in the above-mentioned example, the rapid remelting and rapid resolidification process was performed using a laser beam, but other high-density energy sources such as TIG arc, plasma arc, and electron beam may also be used.

Effects of the Invention This Hikari press molding rough material has a crystal finer layer formed by rapid remelting and rapid resolidification treatment locally only in the area where strength improvement is required, which is the back surface of the J5 pressed product. This method aims to improve the strength locally only in that area. Therefore, a stretchy material is used as the base material to ensure good press formability and prevent cracks and distortions from occurring during press forming. At the same time, it is possible to locally improve the strength of areas where tension rigidity and tent resistance are required, thereby improving the tension rigidity and tent resistance. In addition, when a material with high elongation is used, wrinkles may appear during press molding, but in the material for press molding of the present invention, rapid remelting as described above is applied to the areas where wrinkles are expected to appear.
By forming a crystal-refined layer through rapid resolidification and raising the yield point of that region, wrinkles can also be prevented. Furthermore, this material for press molding by Hikari can obtain good tensile rigidity and tent resistance even if it uses a material with good elongation and good formability as the base material, as mentioned above. It is possible to use inexpensive mild steel materials such as 5CP28 material, which can reduce costs compared to using high-strength steel plates, and even if mild steel materials are used, the Since good tensile rigidity and tent resistance can be obtained without significantly reducing the thickness, weight reduction can also be achieved. Furthermore, a material with good press formability that is less likely to cause cracks can be used as the base material, and as mentioned above, wrinkles can also be prevented, making it possible to prevent cracks and wrinkles in press molds. This makes it possible to reduce the number of man-hours for mold repair and mold design, and because a material with low hardness can be used as the base material, the life of the mold cutting blade can be extended. In addition, with this Hikama press-forming rough material, it is possible to obtain good tensile rigidity and tent resistance as described above without using a high-tensile steel plate with a high content of Mn and P as the base material. Therefore, by using a base material with a low content of Mn, P, etc., it is possible to prevent deterioration in castability when the scrap material is reused as a return material.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an example of a situation in which the rapid remelting-rapid resolidification process applied to the production of press-forming blank material of the present invention is carried out, and Figs. 2 and 3 are illustrations of this explanation. Fig. 4 is a schematic plan view showing the planar shape of the crystal-refined layer shown in the rough material for press molding (6). Figure 5 is a photograph of the cross-sectional structure of the grain refinement layer (400x magnification), and Figure 6 is a photograph of the fFJ Tobe valve partial surface structure. (Magnification: 400x), Figure 7 is a plan view showing the shape of the test piece subjected to the tensile test, Figure 8
Figure (A) is a perspective view showing an example of the rough oxide for press molding of this defense, Figure 8 (B) is a perspective view showing the situation during press molding of Figure 8 (A), Figure 9 is Figure (A) is a perspective view of another example of the blank material for press molding of this defense, and Figure 9 (B
) is a perspective view showing the state of the raw material of FIG. 9(A) after press forming, and FIG. 10 is a side view showing the external shape of an automobile to which the raw material of this explanation is applied. 3... Plate material to be a rough material for press forming, 6. Laser beam with high density energy, 7... Remelting-resolidification bead (crystal finer layer), 10... Rough material for press forming . Applicant Toyota Motor Corporation Agent Patent Attorney 1) Takeru Iriguchi J or 1 person) Ku Aji To Aji Aji

Claims (1)

[Claims] 1. A rough material for press molding, characterized in that a crystal finer layer is locally formed by rapid remelting and rapid resolidification treatment in necessary parts of a surface to be formed into a back surface of a product after press molding.